I am trying to add an action to a button programmatically from within a custom class. However, I keep getting an error when I perform the action. I've read a lot about how to do this but am clearly making a mistake somewhere and can't figure out where.
The button is created in the first instance by dragging it onto the storyboard. I then control drag to the ViewControler.h file to get this:
#property (strong, nonatomic) IBOutlet UIButton *testButtonForClass;
In ViewControler.m, I do this:
- (void)viewDidLoad
{
[super viewDidLoad];
testClass *myClass = [[testClass alloc]init];
myClass.myButton = self.testButtonForClass;
[myClass assignActionTargets];
}
Below is the custom class Header and Implementation file.
Header File
#import <Foundation/Foundation.h>
#interface testClass : NSObject
#property (nonatomic, strong) UIButton *myButton;
-(void)assignActionTargets;
#end
Implementation File
#import "testClass.h"
#implementation testClass
-(void)assignActionTargets{
[self.myButton addTarget:
self action:#selector(myButtonInnerTap)
forControlEvents:(UIControlEventTouchUpInside)];
}
-(void)myButtonInnerTap{
UIAlertView *a = [[UIAlertView alloc]initWithTitle:nil
message:#"testClass says hello"
delegate:nil
cancelButtonTitle:#"Dismiss"
otherButtonTitles:nil, nil];
[a show];
}
#end
You create a testClass instance, but you don't keep a reference to, so it gets deallocated at the end of viewDidLoad.
- (void)viewDidLoad {
[super viewDidLoad];
TestClass *myClass = [[TestClass alloc] init];
myClass.myButton = self.testButtonForClass;
[myClass assignActionTargets];
// myClass gets deallocated here!
}
When the button is clicked, it tries to access the target you specify, but now that's a dangling pointer to an invalid memory segment, hence leading to a crash.
You have to keep a strong reference to myClass in order to keep it alive by the time the button is clicked. Declaring a strong property is a good way of achieving that.
#property (nonatomic, strong) TestClass *myThingy;
- (void)viewDidLoad {
[super viewDidLoad];
self.myThingy = [[testClass alloc] init];
self.myThingy.myButton = self.testButtonForClass;
[self.myThingy assignActionTargets];
}
Code style note: Please, use some naming conventions. Class names should be capitalized (I already changed that in the above snippets, since it kills me...) and using myClass for a pointer to an instance of a class is plain disorienting.
First, the double nil for the argument otherButtonTitles is "problematic". Reduce it to one.
Second, make sure the button and the object is properly retained by your calling class.
Finally, make sure via NSLog or breakpoints that the objects in question (custom object, button) are not nil.
Related
How can I access the value from an inputField located in a second viewController?
The class name of the second view controller is SettingsViewController and the outlet name for the inputField is setRateInput.
I tried this but it didn't work…
double taxRateFromInput = [[self.settings.setRateInput text]doubleValue];
when I NSLog it comes out as The value is: (null)
Any idea what I'm doing wrong?
Here is the implementation file for the main viewController:
#import "SettingsViewController.h"
#interface ViewController ()
#property (strong, nonatomic) SettingsViewController * settings;
#end
#implementation ViewController
// lazy instantiation
-( SettingsViewController *) settings
{
if (_settings == nil) {
_settings = [[SettingsViewController alloc]init];
}
return _settings;
}
- (IBAction)calculatePrice:(id)sender {
double taxRateFromInput = [[self.settings.setRateInput text]doubleValue];
#end
In theory, you could create a global. Create a new class, call it something like taxRate (.h and .m)
In taxRate.h, add the following code:
#import <Foundation/Foundation.h>
#class MyTaxRate;
#interface TaxRate : NSObject {
}
#property (nonatomic, retain) double * taxRateFromInput;
+(TaxRate*)getInstance;
#end
Then, in your controller, put a "#import taxRate.h" in there. In your .m file, add the following:
#import "TaxRate.h"
#implementation TaxRate
#synthesize taxRateFromInput;
static TaxRate *instance =nil;
+(TaxRate *)getInstance
{
#synchronized(self)
{
if(instance==nil)
{
instance= [TaxRate new];
}
}
return instance;
}
#end
Note: This is extremely similar in structure to what I'm purposing.
if you have the reference from the object view controller you can just access by the property from your attribute.
You instantiated a new SettingsViewController, but you didn't do anything to instantiate its textfield setRateInput. You can do it when you instantiate it:
_settings = [[SettingsViewController alloc]init];
_settings.setRateInput = [UITextField alloc] initWithFrame:someFrame]];
or, as a beter solution, instantiate the text field in -init of SettingsViewController
- init {
if (self = [super init] {
self.setRateInput = [UITextField alloc] initWithFrame:someFrame]];
}
return self;
}
If you use nib files, this would be a lot easier.
Note: setRateInput is a bad name for a property. Consider rateTextField instead.
Edit I forgot to add that you have to add the text field as a subview to its parent view.
So it will be like,
_settings = [[SettingsViewController alloc]init];
_settings.setRateInput = [[UITextField alloc] initWithFrame:someFrame] autorelease];
[_settings.view addSubView:_settings.setRateInput];
In this case, the setRateInput is retained by its super view. You're not using ARC, so you can call autorelease on your text field.
The better solution: Use - (void) loadView; inside SettingsViewController. Loading the view is the responsibility of the correspondent view controller.
- (void) loadView {
self.setRateInput = [[UITextField alloc] initWithFrame:someFrame] autorelease];
[self.view addSubView:_settings.setRateInput];
}
Edit: xib files and storyboards can help you out. Give these tutorials a try.
You are on the right track, also well done with your lazy instantiation (as
a demonstration that you grasped the concept, I mean).
But note, that outlets don't get connected until viewDidLoad is called. So if you
just alloc/init your viewController (lazily), the outlet to your textfield is pointing to nil.
The outlet doesnt get connected until your controller's view property is accessed, ie the view is displayed.
What you could do is give the settings viewController a handle to your calculating viewController and let it set a public property on the calculating viewController that represents the rate.
This is a common pattern - delegation - where one viewController (settingsViewcontroller) calls a method on its delegate (calculating viewController).
You wouldn't need the settingsViewcontroller property in your calculating viewController then, but just instantiate a new settings viewController every time you want it to be brought up, giving it a reference to your calculating viewController.
Another possibility - maybe even better - is to define a model object that does calculation and takes care of the rate it needs to calculate. Then you could give your settingsViewcontroller a reference to that model object (probably instantiated in your
other viewController), so that it can change the rate on it.
PS: also re think how you instantiate viewControllers generally. The designated initialiser is -initWithNibName:bundle: - so usually, you wouldn't just alloc/ -init them.
If you use storyboards (you probably should!), use storyboard's -instantiateViewControllerWithIdentifier: or use the above mentioned designated initialiser.
I am passing an NSDictionary object from one view class to another as I transition from a table view to a normal view to show details:
Passing Controller:
[tweetController setTweet:tweet];
Receiving Controller.h:
#interface TweetViewController : UIViewController {
NSDictionary *tweet;
}
#property (nonatomic, retain) NSDictionary *tweet;
Receiving Controller.m:
#implementation TweetViewController
#synthesize tweet = _tweet;
I then try to use this information to set the properties of some fields in my view:
- (void)viewDidLoad
{
[super viewDidLoad];
tweetLabel.text = [_tweet objectForKey:#"text"];
}
The result is a blank label and if I inspect the value of _tweet at this stage it is nil.
I originally had a method which set the value of tweet which I called at the same location as I am now setting the value. If I inspected the value at this stage it was fine.
I presume that the automagic setter through #synthasize is working, but somewhere else the value is being lost.
Sorry this is my first objective C anything! Thanks for any help in advance.
You are using your "tweet" instance variable, whereas the "tweet" property is synthesized to the "_tweet" variable.
You are probably calling the setTweet method after viewDidLoad executes.
I usually pass this kind of thing into a custom init method.
Alternatively, you could do the set before pushing the detail VC onto the nav stack.
Are you sure that tweetLabel isn't nil?
I've made a few corrections & optimisations to your code. You don't need to declare ivars in the header file anymore, they are generated automatically by #synthesize
- (void)dealloc; is only needed if you're not using ARC.
//.h
#interface TweetViewController : UIViewController
#property (strong, nonatomic) NSDictionary *tweet;
#property (strong, nonatomic) IBOutlet UILabel *tweetLabel
#end
//.m
#implementation TweetViewController
#synthesize tweet = _tweet;
#synthesize tweetLabel = _tweetLabel;
- (void)viewDidLoad {
[super viewDidLoad];
self.tweetLabel.text = [self.tweet objectForKey:#"text"];
}
- (void)dealloc {
[_tweet release];
[_tweetLabel release];
[super dealloc];
}
#end
Note: strong is equivalent to retain
To expand on #Rayfleck's answer, since you are new to Objective-C, your custom init method could look like this:
In TweetViewController.h:
- (id)initWithTweet:(NSDictionary*)tweet;
In TweetViewController.m:
- (id)initWithTweet:(NSDictionary*)tweet
{
self = [super init];
if (self) {
_tweet = tweet;
}
return self;
}
and then in your passing controller you'd allocate and initialize like this:
TweetViewController *tvc = [[TweetViewController alloc] initWithTweet:myTweet];
I'm my class i've added a an instance of my view controller, created a property and then synthesized it in my implementation file. I am trying to update the UIlabel in the view controller like this,
NSString *currentChar = [[NSString alloc] initWithFormat:#"%c", ch];
viewController.outputLabel.text = currentChar;
[currentChar release];
My problem is that everything builds without any errors or warnings but the label just doesn't get updated, what am I doing wrong. I'd really appreciate some help on this one.
Are you sure you're referencing the existing viewController and you didn't instantiate a new one? Your property is not declared as copy, correct?
textProcessor.h / .m
#interface textProcessor : NSObject {
MainViewController *mainView;
}
#property (retain) MainViewController *mainView;
#end
#implementation textProcessor;
#synthesize mainView;
MainViewController.h / .m
#interface MainViewController : UIViewController {
UILabel *myLabel;
}
#property (retain) UILabel myLabel;
#end
#implementation MainViewController
#synthesize myLabel;
When you are initializing your textProcessor class, and you set the value for "mainView" like
-(void)viewDidLoad {
[super viewDidLoad];
textProcessor *proc = [[textProcessor alloc] init];
proc.mainView = self;
//note that you are not doing this:
//MainViewController *mainView = [[MainViewController alloc] init];
//proc.mainView = mainView;
//that was creating a new instance variable instead of using self, the existing one
[textProcessor release];
}
Have you created your label in IB? If you are using IB you have to create an IBOutlet for your UILabel. You then make a connection between the UILabel in IB to your IBOutlet in your class.
Have you tried calling the setNeedsDisplay method on the view? Also you may want to try using the setText method instead of assigning directly to the property.
Sorry about the title being extremely vague, I'm new to Objective C and struggling a little with it. Basically I have the following section of code:
Graph *graph1 = [[Graph alloc] init];
[graph1 addNode:#"TEST"];
which is working to a degree. But I want to change it because the above code happens on a button press, and therefore I assume I am creating a new "*graph1" every time I do this. I thought I could simply change it to this:
if(self = [super init])
{
[self setGraph: [[Graph alloc] init]];
}
return self;
Where the above is in the init method, and below is the modified function:
[graph addNode:#"TEST"];
However when debugging I've found addNode method is never called when it's like this.
Thanks
Zac
This is testViewController.h
#import <UIKit/UIKit.h>
#class Graph;
#class Node;
#interface testViewController : UIViewController {
Graph *graph;
UILabel *label;
}
#property (nonatomic, retain) IBOutlet UILabel *label;
#property (nonatomic, retain) Graph *graph;
- (IBAction) buttonPressed:(id)sender;
#end
This is textViewController.m
#import "testViewController.h"
#import "Graph.h"
#implementation testViewController
#synthesize label, graph;
- (id)init
{
if(self = [super init])
{
[self setGraph: [[Graph alloc] init]];
}
return self;
}
- (IBAction)buttonPressed:(id)sender
{
//Graph *graph1 = [[Graph alloc] init];
[graph addNode:#"TEST"];
Node *node1 = [[Node alloc] initWithLabel: #"LABEL"];
label.text = node1.label;
}
The first thing that comes to mind is that graph is nil and thus invoking a method (sending a message) to it will result in nothing. An unwanted release will cause an EXC_BAD_ACCESS, and this seems to be not the case.
I suppose you are calling all of this in a UIViewController subclass, right? Are you sure the right init is called? If you are using a NIB you should override the -(id)initWithNibName:bundle: and place you code there. I guess the code is probably in the plain -(id)init, since you are calling [super init] and not [super initWithNibName:nameOrNil bundle:bundleOrNil], but this way, if initialize the controller with the NIB you custom code is never called and thus graph is nil.
By the way, if the graph property is (retain) you are also causing a memory leak in the init.
I'm sure you're through this problem now, but I agree that the reason "add" is "not being called" is that your graph object is nil at that moment
I'd say, first put a test message around your "addNode" call
NSLog(#"We tried to add here");
[graph addNode:#"TEST"];
That will show you that the add is being called -- I bet it is.
Then, where you had your previous call to initialize "graph" right before your add call, try conditionally initializing it:
if(graph == nil) graph = [[Graph alloc] init];
[graph addNode:#"TEST"];
Note, this is all just to find the problem. Finally I'd say you have some challenges in here with how you are dealing with memory. You may not have reference issues, but later leaks. And depending upon how often this code is executed it could be an issue.
But at least you may get to your issue easier with the above tests.
Have you declared the graph variable in the header? ie: Graph *graph; and the corresponding #property (nonatomic, retain) Graph *graph;
Then I would do this:
-(id) init {
graph = [[Graph alloc] init];
[graph retain];
}
that might help (the only reason I think it wouldn't would be because a) if your variable wasn't declared then you would get a warning like graph may not respond to addNode and if it wasn't retained then your app would crash when it runs)... other than that, I can't see what would be the problem. If that doesn't work, can you please post all your code from your .h and .m files?
Then I would do this:
-(id) init {
graph = [[Graph alloc] init];
[graph retain];
}
that might help
This would result in a memory leak. The retain count of the object pointed to by graph will have a retain count of 2. Not ideal. If you declare the property with the retain attribute then
[self setGraph:[[[Graph alloc] init] autorelease]];
should do it. I go with -
self.graph = [[[Graph alloc] init] autorelease];
There could be many reasons the addNode: method is not being called. Put break points in the enclosing method and see if everything is working as you expect it to.
So, I'm loading by XIB file and it contains a set of UIBarButtonItems. Some of the items are used when the viewDidLoad: is called.
#interface MyViewController : UIViewController {
IBOutlet UIBarButtonItem *addButton;
IBOutlet UIBarButtonItem *editButton;
IBOutlet UIBarButtonItem *doneButton;
}
// NB: There are no properties retaining anything.
#end
#implementation MyViewController
- (void)viewDidLoad {
[super viewDidLoad];
NSArray *initialToolbarItems =
[[NSArray alloc] initWithObjects: addButton, editButton, nil];
self.toolbarItems = initialToolbarItems;
[initialToolbarItems release];
}
- (void)dealloc {
[super dealloc];
// Nothing else to do here since we are not retaining anything.
// … or are we? <insert dramatic music here>
}
#end
If I push the above the above ViewController onto a UINavigationController everything seems fine, all the IBOutlets are assigned and behave like expected.
The instant i pop the ViewController from the navigation stack Instruments' Leaks tells me that I am leaking a UIBarButtonItem. Woe is me!
If I change dealloc: to
- (void)dealloc {
[doneButton release];
[super dealloc];
}
no leaks occur. The same goes if I use doneButton in viewDidLoad:
NSArray *initialToolbarItems =
[[NSArray alloc] initWithObjects: addButton, editButton, doneButton, nil];
My question: Why is my IBOutlet leaking when I don't use it. I don't retain it at any point. The the NIB loader should own the object, right?
Only thing I can think of:
The nib loader treats IBOutlets as strong references. All outlets are retained by default unless you specifically indicate assign. So you still need to release them in dealloc and viewDidUnload.
You can also use a assigned property to make it a weak reference:
#property (nonatomic, assign) IBOutlet UIBarButtonItem *doneButton;
Some reading: http://weblog.bignerdranch.com/?p=95
If you have #property with (retain) declared for the your IBOOutlets they will be retained and must be released
The array retains them